1. Field of the Invention
The present invention relates to a wastegate valve controller provided in an internal combustion engine including a supercharger such as a turbo charger.
2. Description of the Related Art
To date, there has been known a technology in which in order to raise the output of an internal combustion engine, a turbo charger is provided in the intake path of the internal combustion engine and in which intake air in the intake path is supercharged with the turbo charger so as to be supplied to the internal combustion engine. A turbo charger is to rotate a turbine with exhaust gas from an internal combustion engine and apply pressure to air to be supplied to the internal combustion engine; however, when the internal combustion engine is under the condition of a high rotation and a high load, the supercharging pressure may unnecessarily increase, thereby breaking the internal combustion engine.
Accordingly, in general, an exhaust gas bypass for bypassing part of exhaust gas to be supplied to the turbine is provided in an exhaust path, and the amount of bypassed exhaust gas that enters the exhaust gas bypass is controlled with a wastegate valve (also referred to as a W/G valve, hereinafter) so that the inflow amount of the exhaust gas to the turbine is adjusted, thereby controlling the intake air pressure (supercharging pressure) to be at an appropriate level.
In general, a W/G valve is driven by use of a positive-pressure actuator. This actuator is coupled with an intake path of an internal combustion engine, especially, with an intake path at the upstream side of a throttle valve, the pressure in which particularly increases; when the pressure in the intake path of the internal combustion engine becomes higher than the atmospheric pressure, the operation of the actuator is enabled.
In general, the W/G valve is kept off until the operation of the actuator is enabled.
With the configuration of a conventional W/G valve controller formed as described above, the W/G valve cannot be operated unless the pressure in the intake path of the internal combustion engine increases; therefore, when the pressure in the intake path is the same as or lower than a predetermined value, the W/G valve cannot be operated even if there exists a demand for changing the W/G valve opening degree.
Accordingly, in recent years, there has been proposed a system in which there is adopted an electric W/G drive method in which a W/G valve is driven by a motor and, regardless of the pressure in the intake path, the W/G valve is operated when required so that the supercharging by the turbo charger is limited, thereby improving the gasoline mileage (refer to, for example, Patent Document 1). The conventional apparatus makes it possible that when the load on the internal combustion engine is low, the opening degree of the W/G valve is increased to lower the exhaust pressure and to reduce the pump loss of the turbo charger so that the conventional apparatus can contribute to improvement of the gasoline mileage.